1. Field of the Invention
The present invention relates to the field of technology which is known as encapsulation. This concept relates to the protection of devices such as, for example, solid-state integrated circuits, electromechanical relays, piezoelectric resonators against the various causes of degradation resulting from the environment.
2. Description of the Prior Art
Two main causes of degradation are observed in practice, one cause being related to such phenomena as chemical corrosion, oxidation by atmospheric oxygen, acid or basic atmospheres, salty air, and the other cause being related to water vapor.
In all cases, the solution to the problem is obtained by enclosing the device to be protected within a leak-tight case which is usually designated as a package.
Furthermore, since the choice of the internal gas atmosphere can be freely determined, the package may accordingly be filled with a chemically neutral gas such as nitrogen, helium, or a helium-neon mixture. In certain applications such as electron tubes, for example, it is even possible to produce a high vacuum of the order of 10.sup.-6 mm of mercury.
For the practical construction of packages, either a metal or a glass has been employed up to the present time. In either case, a package has been formed by assembling and welding a cover on a base after the device to be encapsulated has been fixed on the base.
However, it has been found that, during utilization of the device which has thus been encapsulated, the composition of the internal atmosphere varies with time while impurities such as traces of ambient air as well as water vapor which remain after closure are progressively released into the external atmosphere. These impurities are retained on the internal face of a package as a result of absorption and adsorption phenomena in proportions which are much higher in the case of metal surfaces than in the case of glass surfaces, for example.
In practice, in spite of the advantages offered by glass packages, the most widespread industrial practice consists in utilizing packages of metal having good weldability such as copper or steel and coated with layer of metals which do not readily oxidize such as nickel, gold or a succession of the two, or the alloy of copper, nickel and zinc known as German silver in which the proportion of zinc has been maintained at a low value.
In comparison with devices of the prior art, the package in accordance with the invention offers many advantages including in particular:
the advantage of resistance to high temperatures;
the advantage of being sealed by the so-called cold welding process which does not produce any stress at the time of welding.